NCAR Airborne Oxygen Instrument (AO2)

1. NCAR Airborne Oxygen Instrument (AO2) Flow control: • Vacuum ultraviolet absorption technique • Xe lamp (147 nm) and CsI detector • Adapted from shipboard design (Stephens et al., 2003) • Active pressure and flow control to 10-6 • Switches every 2.5 seconds between sample and WT gas • 5-second 1-sigma precision of ± 2 per meg • Factor of 2-5 motion degradation is correctable O2 sensor

2. NCAR Airborne Oxygen Instrument (AO2) System components: (fridge trap)

3. HIPPO1 Profile at 65 S Southern Ocean O2 outgassing January 20, 2009

5. (shorter preflight flow period)

6. (fridge trap + pre- and post- flight dry air purge)

7. (after linear time-in-flight correction)

8. per meg Atmospheric Potential Oxygen: APO = O2 + 1.1*CO2

13. Summary • AO2 has operated on every flight • HIPPO1 RF02 CO2_AO2 suffered from a cabin pressure effect and is not reported • HIPPO3 RF06 O2_AO2 has several hours of missing data due to a noise problem • HIPPO2 and HIPPO3 CO2_AO2 quality is degraded by inlet humidity effect and not useful for rigorous comparison to other sensors • O2_AO2ADJ and APO_AO2ADJ are recommend variables for O2 analyses Between now and HIPPO4 • Laboratory experiments to characterize inlet humidity effects on O2 and CO2 • Software improvements to reduce remaining motion sensitivity

14. HIPPO1 descent into ANC

15. NCAR Airborne Oxygen Instrument (AO2) 8-hour flight 3-min cal

16. NCAR Airborne Oxygen Instrument (AO2) • Inlet delay ~ 40 seconds with only a few second altitude dependency • Checked against OMS and VCSEL for 10 low and 10 high-alt transitions per flight

19. HIPPO1 Profile at 80 N January 12, 2009